Lipase catalyzed interesterification of palm stearin and rice bran oil blends for preparation of zero trans shortening with bioactive phytochemicals

Abstract

Palm stearin (PS) and rice bran oil (RBO) blends of varying proportions were subjected to enzymatic interesterification (EIE) using a 1,3 specific immobilized lipase. The interesterified blends were evaluated for their physicochemical characteristics and bioactive phytochemical contents using differential scanning calorimeter (DSC), X-ray diffraction (XRD), gas chromatography (GC) and high performance liquid chromatography (HPLC). The blends of PS and RBO in different proportions (40:60, 50:50, 60:40 and 70:30) had saturated fatty acid content and unsaturated fatty acid content in the range of 37.6–52.0% and 48.0–62.4%, respectively. The blends 40:60, 50:50 and 60:40 showed a considerable reduction in their highest melt peak temperature (T_P) and solid fat content (SFC) on EIE. The interesterified blends retained bioactive phytochemicals like tocols (839–1172 ppm), sterols (4318–9647 ppm), oryzanols (3000–6800 ppm) and carotene (121–180 ppm). XRD studies demonstrated that the interesterified blends contained β and β′ polymorphic forms.

Introduction

Integrated processing of bioresources for optimal utilization has been gaining serious attention today for competitiveness and environmental protection. Cereals, oil seeds, fruits and vegetables are processed in large volumes resulting in huge amounts of by-products that are currently underutilized because of the inadequacy of conventional technologies. For example, about 600 million metric tones (MMT) of rice is produced annually in the world and the rice bran produced as a by-product of rice milling is about 40 MMT with about 15–22% oil (Arumughan et al., 2004). Rice bran thus has potential of 6–8 MMT healthy edible oil and bulk of it is utilized for low value cattle and poultry feed. With about 130 MMT annual production, India is the second largest rice producer in the world and the estimated availability of bran is 10 MMT. Utilization of rice bran in India for oil extraction is comparatively efficient (50–60%) as compared to that of other major rice producing countries (Tikkoo et al., 1998). Bulk of the crude rice bran oil is currently used for blending with other edible oils due to poor colour value on refining. Crude rice bran oil is extremely rich in bioactive phytochemicals such as γ-oryzanol, phytosterols and tocopherol/tocotrienols (tocols) with proven health benefits. γ-Oryzanol is unique to rice bran oil (RBO) and are potent hypocholesteremic agents. The tocotrienols that comprise 70% of the tocols in crude rice bran oil have been shown to be powerful antioxidants and antithrombotic agents (Arumughan et al., 2004, Mayamol et al., 2004). RBO thus could be an ingredient for nutritional shortenings. There is a trend towards utilization of vegetable oil based shortenings without hydrogenation to avoid trans fatty acids (TFA). In the past few years, several nutritional studies have suggested a direct relationship between TFA and increased risk for coronary heart disease (Tarrago-Trani et al., 2006). Consequently efforts have been made to replace hydrogenated oils by other hard fat to reduce TFA intake through shortenings. For producing shortenings with desired functional properties, the essential requirement is an appropriate blend of liquid and solid fats. Palm stearin (PS) in this context deserves attention as a potential hard fat of vegetable origin to replace hydrogenated fat. PS is obtained in the process of producing palm olein from the semi-solid palm oil by fractionation. The high melting fraction of PS with melting point ranging from 45 to 55 °C is non-edible. However it could be appropriately blended and interesterified with liquid oils in order to modify the physical characteristics to meet the functional properties and the quality required for shortening through interesterification. Currently about 7 MMT PS is produced globally, most of which is used by the oleo chemical industries. Utilization of PS for making shortening without TFA is not only to achieve value addition but also to address the adverse health effects of TFA. Different processes are currently available for the production of zero trans shortening which include chemical or enzymatic interesterification. Chemical interesterification (CIE) having the disadvantages of cleaning process to remove the residual catalyst besides the formation of undesirable products is being replaced by enzymatic process. Ecofriendly processes for modifying fats and oils by utilizing lipases from different microbial origin have therefore been reported by various researchers (Husum et al., 2004, Ronne et al., 2005). Attempts have also been made in interesterifying liquid oils like rapeseed oil, soy bean oil, olive oil with butter fat, PS and partially hydrogenated oil, respectively (Ronne et al., 2005, Osorio et al., 2005, Alpaslan and Karaali, 1998). We have reported utilization of RBO and PS as a simple blend without interesterification for production of trans free shortenings of high nutritional value (Mayamol et al., 2004). An improved process using ecofriendly enzymatic interesterification (EIE) has been employed in the present work. RBO was selected as the liquid oil for its exceptionally rich bioactive phytochemicals and balanced fatty acid composition and PS for its ability to contribute solid fat content in the shortening and also to provide naturally present carotene at high concentration which is unique to palm oil. The objective of such an ideal blend coupled with enzymatic process was to produce a variety of shortenings through judicial blending and manipulation of regiospecificity of lipase catalyst which depends largely on the oils/fats used in the blend. Enzymatically interesterified products obtained under different conditions were evaluated for their functional properties and retention of micronutrients and are reported in this paper.